1. Field of the Invention
The present invention relates to directional boring systems, and more particularly to the boring head to boring hit interface thereof.
2. Description of the Prior Art
Directional boring has become increasingly important for the installation of underground cables, such as for example electric, cable television, and telephone cables.
An example of a prior art directional boring system 10 is shown (in part) at FIGS. 1 and 2, wherein a spindle drive of a directional boring apparatus 12 serves to rotate and push drill pipe 14 into the ground G. As best shown at FIG. 2, at the end of the drill pipe 14 is a threadably mounted boring head 16 and a boring bit 18 connected to the boring head by bolts 20. The boring head 16 has a bit connection face 22 which has an acute angle A' with respect to the pipe axis P. The boring bit 18 may have various shapes for cutting into soil wherein a head connection face 24 is configured to restably mate with the bit connection face 22 of the boring head 16.
The drill pipe is hollow and is connected to a supply of high pressure water from the directional boring apparatus 12. The boring head 16 has an interior hollow which communicates with a hollow threaded shank 16a thereof. The boring head 16 further has a nozzle 26 through which the high pressure water from the directional boring apparatus 12 exits. The boring bit 16 is provided with carbide hard-facing 28 at the cutting edges for providing enhanced abrasion resistance during boring operations.
In operation of a directional boring system, the directional boring apparatus 12 forces the boring bit 18 into the ground G. The high pressure water serves to open the ground and help make way for the advancement of the boring bit and its associated boring head. The acute angle of the boring bit is adjusted relative to the ground (it is now not rotating) so that the boring head descends to a predetermined depth and then attains a horizontal attitude. The drill pipe 14 is now caused to rotate and with the advancement force supplied by the directional boring apparatus on the drill pipe, along with the high pressure water stream from the nozzle, the drill pipe advances underground along a predetermined path at the predetermined depth. More drill rods are added to assure sufficient drill pipe for the job, which can exceed a drill path length of 300 feet. When the end of the path is approaching, the drill pipe is again stopped from rotating and the acute angle of the boring bit is adjusted to cause further advancement to result in ascension until the boring head breaks ground. Now, a hook is installed on the boring bit and the directional boring apparatus now pulls back the drill pipe, wherein the cable is attached to the hook and is fed into the underground passage made by the drilling operation.
Thrust supplied by the directional boring apparatus can reach 17,000 pounds and the rotation speed of the boring bit can reach 200 revolutions per minute. Although the water flow rate out the nozzle can reach 700 pounds per square inch at a flow rate of up to 25 gallons per minute the boring bit is subjected to extreme shear force as it rotatively cuts into soils. When rocky, hard soils are encountered, such as glacial till soil, the boring bit can be subjected to shearing shock forces. Whatever the source, shearing forces tend to dislodge the boring bit from the boring head. Since only the bolts secure the boring bit to the boring head, these bolts must resist these shearing forces. No matter whether three, six, eight or more bolts are used, the bolts eventually will break, usually unpredictably, and always with great waste of time and expense for the directional boring system operator.
One attempt to address these problems has been devised in which a rectangular plate is bolted to the end of the drill pipe 14, with the opposite end of the plate overlaying and covering the bolts 20 used to secure the boring bit to the boring head. While this approach provides some protection for the bolts, the sides and surface of the boring head opposite from the plate as well as the sides of the boring bit remain exposed and are subject to abrasion and wear during drilling operation.
Accordingly, what remains needed in the art is an interface for a boring bit to a boring head, wherein shear force to the bolts is relieved and the boring head and the boring bit are protected from abrasion and wear during drilling operations.